A method of reading multimedia information, an apparatus for reading multimedia information, a storage medium drive device, a transfer medium, an information stream, and an electronic device
The present invention relates to a method and an apparatus for reading mixedly first information such as video information, audio information, or the like for which guarantee of response time is important, and second information such as electronic program table data or the like for which reliability is important, from a storage medium such as a hard disk or the like.
A system which reads data from a random-accessible storage medium such as a hard disk or the like normally comprises a storage medium drive section such as a hard disk drive, and a host computer section for sending a read command to the storage medium drive section thereby to control execution of data reading. The storage medium drive section and the host computer section are separate from each other in some cases, or the storage medium drive section is included in the host computer.
Conventionally, in this kind of system, the data to be read from the storage medium is mainly data used for calculations or the like in the computer, and reliability of the data is important. Therefore, the response time taken to transfer data from the storage medium drive section to the host computer side in response to a read command from the host computer side is considered as being much less important in many cases.
That is, upon receipt of a read command from the host computer section, the storage medium drive section accesses a storage medium any number of times until errors are lost, to read correct data and transfer it to the host computer section side.
In recent years, a random accessible storage medium such as a hard disk, DVD (Digital Versatile Disk or Digital Video Disk), or the like has come to be able to store a large amount of data. From this background, a data reading apparatus has come to deal with not only data (which will be hereinafter called IT (Information Transfer) data) used for computer programs and calculations, as in a conventional apparatus, but also video data and audio data (which will be hereinafter called AV (Audio and Visual) data).
A conventional data reading apparatus, however, does not adopt a method in which AV data and IT data are not differentiated from each other and the response time of data is much less important.
Meanwhile, characteristics required for the host computer section and the storage medium drive device such as a hard disk drive or the like are different from each other, depending on the application use of data.
Conventionally, opportunities for data access to the IT data and that to the AV data are determined as coming at the same time for a small number of times. Classification of characteristics with respect to data access is as shown in the table shown in FIG. 1.
That is, the following characteristics are required for access to AV data.
Re: Continuity of Data Output
In order that a user can watch and listen to AV data (on real time) while it is being read out, seamless playback is most important.
Re: Reliability of Data Contents
AV data has a characteristic that quality sufficient for watching or listening to the data can be maintained in many cases even when AV data contains much or less errors. However, since a certain part of AV data consists of a kind of data (e.g., time stamp, format information, or the like) which is important to play back a video image or sound, reliability concerning data contents is important with respect to this part.
Meanwhile, the following characteristics are conventionally required with respect to access to IT data, as shown in FIG. 11.
Re: Continuity of Data Output
There are conventionally fewer application uses of IT data for real-time providing to users, and therefore, continuity of data output is not required.
Re: Reliability of Data Contents
IT data always requires reliability at 100%. That is, the reliability concerning data contents is most important for IT data.
Differentiation of characteristics between conventional AV data and IT data described above exists on the basis of prerequisite that there are fewer opportunities for accessing IT data and AV data.
In recent years, however, there appears a system which issues access to IT data during a sequence of access to AV data. For example, there has been a proposal for an apparatus which enables time-shift monitoring in an apparatus such as a household set-top box, owing to realization of digital TV broadcasting and appearance of a storage medium having a large capacity such as a hard disk which enables random access.
This apparatus comprises, for example, a hard disk apparatus section and a host computer section, so that broadcasting programs to be watched and listened to, EPG (Electrical Program Guide; electronic program tables) appended to programs, World Wide Web information (Hyper Text Makeup Language information), and the like are previously taken into a hard disk having a large capacity. Further, a user accesses the hard disk in the hard disk device section through the host computer section later, to watch and listen to his or her favorite programs at a preferable time or to watch or record EPG or Web information into a VCR (Video Cassette Recorder).
In this kind of apparatus which enables time-shift monitoring, for example, EPG or Web information is displayed while watching and listening to a predetermined TV program, to watch the contents of the EPG and Web information, or EPG is displayed on the screen while recording a certain TV program. Thus, various application uses are proposed. Therefore, there appears a situation that access to IT data such as EPG occurs during a sequence of access to AV data for watching and listening to a TV program.
Thus, if access time for IT data is not guaranteed in a system which issues access to IT data during a sequence for accessing AV data, there may be a case that access to AV data coming next cannot be executed in accordance with a schedule of the host computer.
That is, for example, in the time-shift monitoring as described above, access for obtaining EPG data continues until correct data of EPG is outputted from a hard disk, if EPG data contains an error when the EPG data is accessed during a sequence of accessing AV data to watch and listen to a broadcasting program by a conventional access method which does not guarantee access time.
FIG. 2 shows the data stream of the sequence at this time. Although data is read from the hard disk in units of predetermined amounts in response to a read command from the host computer section, there is no time guarantee with respect to EPG data, and therefore, the host computer section continues accessing the hard disk with respect to EPG data any number of times until no errors are detected the EPG data contains errors. In this situation, AV data is interrupted during the time period in which the EPG data is being accessed.
Hence, in case where IT data is thus accessed in an access sequence for a series of AV data and AV data and IT data are read out mixedly from the hard disk, a conventional method of differentiating data, described above and shown in the table in FIG. 1, is not required but differentiation concerning IT data to be accessed mixedly together with AV data is required. That is, continuity of data is an indispensable requisite with respect to IT data in this case.
As described above, basically, time guarantee is not achieved with respect to data access in a data reading apparatus used in a conventional system, but normally, only the reliability concerning data contents to be outputted is taken into consideration. It is not possible to perform processing corresponding to noble data access as shown in FIG. 12 described above. In addition, even if it is tried to take in the concept of time guarantee, only same commands (or protocol) can be used with respect to recording/reproducing from the host computer, and therefore, flexible access corresponding to the characteristic of each data cannot be realized.
Hence, to process AV data which requires response time guarantee, a buffer memory having a large capacity is conventionally provided in the storage media drive side so that data to be continued might not be interrupted.
In this method, however, the storage media drive side requires a buffer memory having a large capacity, resulting in a problem that the system cost increases. In particular, when a data reading apparatus is mounted in a household AV electronic apparatus, this problem is as large as cannot be neglected.
Even if a buffer memory having a large capacity is provided, data continuity is not essentially guaranteed by the data reading apparatus, and therefore, the possibility of causing an interruption of video data and a jump of sound data cannot be neglected though its provability of occurrence is low. In particular, the transfer rate required for AV data dealt with by the digital AV system has become high in recent years.
For example, a so-called DV (Digital Video) format which has come to be used generally requires a transfer rate of about 30 Mbps, and a memory of at last 60 Mb is required to prepare a buffer for two seconds in the system side, so that increase of the cost is a serious problem. For example, if three seconds are taken to attain an access result as a result of repeatedly trying to read data in a hard disk or the like with respect to access AV data, continuity of AV data cannot be guaranteed even with the system as described above.
Meanwhile, if case of using a data reading apparatus which simply guarantees the access time but does not guarantee the reliability of data contents, the apparatus functions to a certain extent but a problem occurs when access is made mixedly together with IT data which indispensably requires reliability concerning data contents, with respect to access to AV data. Further, with respect to AV data, a part of data includes a portion whose contents are taken as being important as described above, and therefore, all reliability concerning data contents cannot be unnecessary.
The present invention has an object of providing a method of reading multimedia information capable of optimal data access and an apparatus thereof, in view of the above-mentioned points and in consideration of the kinds and contents of data to be accessed and further the relationship with other data during access.
To solve the above problem, in the method of reading multimedia information according to claim 1 of the present invention, first information for which response time guarantee is important and second information for which reliability is important are read from a storage medium, with the first information and the second information mixed with each other, wherein management of read time is performed not only on the first information but also on the second information.
According to the invention constructed as described above, management of the read time is carried out for the second information such as IT information or the like for which reliability is important. It is possible to avoid interruption of the continuity of the first information such as AV data or the like for which response time guarantee is important.
In the invention described in claim 2, in the method according to claim 1, each of the first information and the second information is read in units of predetermined amounts, and a maximum value of a read time for the unit of the predetermined amount is set to manage the read time.
According to the invention described in claim 2, information is read in units of predetermined amounts, and the information read time can be managed with the maximum value of the unit of the predetermined amount used as a limit value. It is therefore possible to guarantee maintenance of the continuity of the first information and the second information.
Further, in the invention described in claim 4, in the method according to claim 2, a plurality of error countermeasure processing methods are previously defined in case where an error occurs in information read out when reading the first or second information in units of the predetermined amounts, and when reading the first or second information, which of the plurality of error countermeasure processing methods should be used is set.
In case where time management is performed on the second information, an error countermeasure processing method is always required for the case where correct information could not be obtained within a management time. According to the invention described in claim 4, however, a plurality of error countermeasure processing methods are previously defined, and any one selected from the plurality of error countermeasure processing methods can be set when reading the first information and the second information. Therefore, it is possible to carry out read processing matched with the characteristics of the first information and the second information.
As has been explained above, according to the present invention, it is possible to provide a method and an apparatus for reading multimedia information, which are capable of making optimum data access in consideration of the type and content of data to be accessed and the relationship to other data during access. In addition, a buffer having a large capacity is not required in the side of the storage media drive.